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Warming indirectly simplifies food webs through effects on apex predators.
Eoin J O'Gorman1, Lei Zhao2, Rebecca L Kordas3
1School of Life Sciences, University of Essex, Colchester, UK. e.ogorman@essex.ac.uk.
Nature Ecology & Evolution
|October 5, 2023
Summary
Warming amplified fish predator effects on freshwater ecosystems, altering food webs and nutrient cycling. These interactive effects highlight the importance of considering both warming and species interactions for predicting ecological impacts.
Area of Science:
- Ecology
- Environmental Science
- Aquatic Ecosystems
Background:
- Global warming impacts ecosystems through direct physiological effects and indirect biotic interactions.
- The relative importance of these effects in natural settings remains unclear due to experimental challenges.
- Freshwater ecosystems are particularly vulnerable to warming and alterations in predator-prey dynamics.
Purpose of the Study:
- To investigate the interactive effects of warming and apex fish predators on freshwater ecosystem structure and function.
- To determine how temperature influences the cascading effects of predators in a natural stream environment.
- To assess the combined impact of warming and predation on food web dynamics and nutrient cycling.
Main Methods:
- Field experiments were conducted along a natural stream temperature gradient.
- Manipulative experiments assessed the effects of warming and the presence of apex fish predators.
- Measurements included algal production, microbial decomposition, and food web structure (connectance, mean trophic level).
- A mechanistic model was used to understand the drivers of observed changes.
Main Results:
- Apex fish predators exerted cascading effects on algal production and microbial decomposition, but only under warming conditions.
- Neither warming nor fish presence alone altered food web structure.
- Combined warming and fish presence led to a decline in food web connectance and mean trophic level due to consumer species loss.
- Altered species interactions were identified as the primary driver of the temperature-induced trophic cascade.
Conclusions:
- Warming significantly modifies the impact of apex predators on freshwater ecosystems.
- The interactive effects of warming and predation can lead to substantial changes in food web structure and function.
- Ecological predictions of warming impacts should incorporate biotic interactions and food web dynamics to avoid underestimation.
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